Magnetic keys

ABSTRACT

A magnetic key suitable for use with electronic equipment comprises a magnetically controllable semiconductor device mounted between two soft iron pole pieces, and a permanent magnet movable relative to the device. The magnet is carried by a slide movable between two positions and biased by a spring towards one of the positions. In one position only a substantial part of the magnetic flux of the magnet passes through the device, so the condition of the device can be controlled by movement of the slide.

United States, Paten 1151 3,668,596 Hubrlc i 1451 June 6, 1972 [5 1MAGNETIC KEYS [56] References Cited UNITED STATES PATENTS [72] Inventor:Rudolf l-lubrich, Ravensburg, Germany 3,571,774 3/1971 l-lubrich..338/32 R 1 Asslsnw kalmufld Fmslerholll Elektrotech- 3,590,134 6 1971Ogi ..338/32 R x n1sche spezlalfabrik, Ravensburg/Wun- I tgmberg GermanyI Primary Examiner-C. L. Albritton Filed: o. 1970 Attorney-Emest S.Montague [2l] Appl. No.: 83,753 [57] ABSTRACT A magnetic key suitablefor use with electronic equipment comprises a magnetically controllablesemiconductor device [30] Foreign Appnmhon Pnomy Data mounted betweentwo soft iron pole pieces, and a permanent July I, 1970 Germany G 70 246434 magnet movable relative to the device. The magnet is carried by aslide movable between two positions and biased by a 52 us. c1. ..338/32R 323/94 11 324 46 swing a 51 1111.01 .3 .1166 7/16 stamial magneic fluxmagnet Passes mush 581 Field of Search ..338/32 R, 32 11; 323/54 1-1-device can be by 324/45, 46; 335 1; 307 309; 317 235 H mwemen Slide- 10Claims, 3 Drawing y BACKGROUND OF THE INVENTION Numerous differentembodiments of magnetic keys, particularly, but not exclusively,designed to be fitted in electronic equipment, are already known. Theinvention relates specifically to such keys in which a change in theposition of a magnet relative to a magnetically controllablesemiconductor device produces a change in the electrical resistance ofthe semiconductor device. So-called field plates have already been usedfor this purpose; with these, the electrical resistance is known todepend on the strength of the magnetic field permeating them. 7

SUMMARY OF THE INVENTION One object of the present invention is toprovide a new or improved magnetic key.

Another object of the present invention is to provide a particularlyadvantageous form of magnetic key, which is simple and therefore cheapto produce, and with which good durability and great security ofoperation is also obtained.

According to the present invention there is provided a magnetic keycomprising a casing, a slide mounted in the casing for linear movementbetween two positions, spring means urging the slide towards one of saidpositions, apermanent magnet carried by the slide and having a Northpole and a South polealigned in the direction of said movement of theslide, two pole pieces mounted within the casing, a magneticallycontrollable semiconductor device mounted between the pole pieces, thearrangement being such that in one of said positions of the slide saidtwo poles of the magnet are adjacent to the two pole piecesrespectively-whereby a substantial part of the magnetic flux of themagnet passes through said device, and in the other of said positions ofthe slide said two poles of the magnet are both adjacent to one of thetwo pole pieces.

The result is that in one of said positions of the slide themagnetically controllable semiconductor device is permeated 4 by a manytimes stronger magnetic field'than in the other of said positions. Theelectrical resistance of the device is consequentlydependent on theposition of the slide, and this physical effect can be used in knownmanner to generate electric switching pulses. 5

The casing is preferably of plastics material and has on the inside twogrooves disposed parallel to said direction, and the slide is providedwith two rib-like projections slidable in respective grooves.

It is advantage for the two pole pieces to be plate-shaped and made ofmagnetically soft iron.

In a preferred embodiment of the invention said device is plate-shaped,the end faces of the two pole pieces which face towards one another areparallel with one another and substantially perpendicular to saiddirection, and the two large surfaces of said device extendperpendicular to said direction.

In order to make maximum use of the flux emanating from the permanentmagnet, it has been found desirableto taper the cross section of onepole piece in the direction of said device preferably to less than half.

Naturally, it will be appreciated that many variations may I be effectedwithout departing from the spirit and scope of the present inventiveconcept.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal sectionthrough the key; FIG. 2 is a section on the line A'B of FIG.. I; and FIG. 3 is a constructional detail on a larger scale.

'2 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, themagnetic key comprises a plastics case 1, in which a plastics slide 2,arranged at right angles, is movably mounted and linearly displaceableagainst the force of a spring 3 between two limit positions. As can beseen clearly from FIG. 2, the slide 2 is provided on two opposite sideswith projecting ribs 4 and 4', respectively; the ribs 4 and 4 beingguided in corresponding grooves 5 and 5 respectively in the case 1. Theslide 2 carries a generally U-shaped permanent magnet 6 with its Northand South poles aligned on behind the other in the direction of movementof the slide 2. Within the case 1, in the region of the magnetic fieldof the permanent magnet 6, is mounted a magnetically controllablesemiconductor device 7, which, during operation, has a current flowingthrough it. The electrical resistance of the device 7 can be varied byvarying the strength of the magnetic field in which it is disposed. Suchdevices are commercially obtainable, for example, under the name offield plates. The device 7 is secured between the soft iron plates 9 and9'.

By providing appropriate stops or by suitably shaping the case 1 and/orthe slide 2, the displacement path of the slide 2 is limited, so that,in one limit position, that is the inoperative position which is shownin FIG. 1, the slide 2 is urged upwardly (as viewed in FIG. 1) by theforce of the spring 3. By pressing a knob 10 fixed on the slide 2, theslide 2 can be moved into the other limit position. The device 7 is somounted relative to the magnet 6 that in the first-mentioned position ofthe slide 2 a far larger proportion of the magnetic flux between thepoles of the magnet 6 flows through the device 7 than in the otherposition of the slide 2.

In FIG. 1 position substantially all the magnetic flux of the magnet 6passes through the device 7, the plates 9 and 9 acting as pole piecesand concentrating the flux through the device 7. When the knob 10 isdepressed, the magnet 6 will be disposed such that the plate 9' extendsacross both poles of the magnet 6, so that substantially all themagnetic flux passes through the plate 9', and so does not pass throughthe device 7. When the knob 10 is depressed, the ohmic resistance of thedevice 7 is thus changed, and this can be caused to generate a switchingpulse. For this purpose, the device 7 is coupled via connecting leads(not shown) to the control circuit of a logic element mounted on asupport 1 1.

It is preferable for the device 7 to be in series with an ohmic resistorin a voltage divider circuit, and for the connecting point to be coupledto the control electrode of a transistor. The parameters are selectedsuch that a change in the ohmic resistance of the device 7 will sochange the potential of the control electrode of the transistor that thetransistor passes from the blocked to the conductive state or viceversa. A material which has proved particularly successful for themagnet 6 is ALNICO 450.

FIG. 3 is a side view on a larger scale of the plates 9 and 9'. Betweenthe two plates 9 and 9' is the device 7, the top and bottom end faces ofwhich (as viewed in FIG. 3) have, in one embodiment, the dimensions 1.7X 3.7 mm. The active surface on the top of the device 7 has thedimensions 0.7 X 1.7 mm. In order that the magnetic flux of the magnet 6can be utilized as effectively as possible, that is supplied via theplates 9 and 9 to the active surface of the device 7, the end of theplate 9 abutting the device 7 is tapered to one third of the area of thenon-tapered cross section of the plates 9. In the example illustrated,the thicknesses of the plates 9 and 9 are 0.8 and 1.5 mm respectively,while both plates 9 and 9' have a width of 45 mm (in the non-taperedportion). An angle of 45 has been found useful for the wedge-liketapering of the plate 9.

In the embodiment illustrated, displacement of the knob 10 and of themagnet 6 coupled thereto causes the ohmic resistance of the device 7 tobe changed in the ratio 1:5. This change in resistance, obtained withsimple means, is not merely adequate for virtually all fields ofapplication, but also ensures security of operation.

Many possible modifications will become apparent from the foregoingwithout departing from the spirit of the present invention. However, theforegoing disclosure is presented in an illustrative sense rather than alimiting'sende and the appended claims are relied upon to definethescope of the present-invention.

What is claimed as new and desired to beprotected by Letters Patent isset-forth in the appended claims.

What isclaimed is:

I 1. A magnetic key comprising a casing, a slide mounted in the casingfor linear movement between two positions, spring. means urging theslide towards oneof said positions, a .permanent magnetcarried by theslide and having aNorth'pole and a South pole aligned'in the direction'of'saidmovement of the slide, two pole pieces mountedwithin the casing,a magnetically'controllable semiconductor device mounted between thepole pieces, the arrangement being'suchthat in one of said positions ofthe'slide said two poles of the magnet are adjacent to the two polepieces respectively whereby a substantial partof the magnetic fluxof themagnet passes through said device, and in the other of said positions ofthe slide said-two poles of v the magnet are both adjacent to one ofthe'twopole pieces.

2.-A key according to claiml wherein the casing is made'of plasticsmaterial.

3. A key accordingto claim Zwherein the casing has on the inside twogrooves disposed parallel to 'said direction, and the slide is providedwith two rib-like projections slidable in respective grooves.

4. A key according to claim 3 whereinthe slide is made of plasticsmaterial.

5. A. key according to claim 1 wherein the magnet is generally U-shaped.

6. A key accordingto claim 1 wherein the two pole pieces areplate-shaped and made of magnetically soft iron.

7. A key according to claim 6 wherein one polepiece, as measured in saiddirection, is substantially longer than the other pole piece, and. saidone pole piece is arranged in the casing such that in said other of saidpositions of the slide said twopoles of the. magnet are both adjacent tosaid one pole piece.

8: A key according to claim 7 wherein the end faces of the two polepieces, which face towards one another, are parallel with one anotherand substantially perpendicular to said direction, said device inplate-shaped, and the two large surfaces of said device extendperpendicular to said direction.

9. A key according to'claim.8 wherein the cross section of one polepiece is taperedin the direction of saiddevice.

10. A key according toclaim 9: wherein the end face of the taperedpolepiece has at most one third of thecross-sectional area of thenon-tapered part of said pole piece.

1. A magnetic key comprising a casing, a slide mounted in the casing forlinear movement between two positions, spring means urging the slidetowards one of said positions, a permanent magnet carried by the slideand having a North pole and a South pole aligned in the direction ofsaid movement of the slide, two pole pieces mounted within the casing, amagnetically controllable semiconductor device mounted between the polepieces, the arrangement being such that in one of said positions of theslide said two poles of the magnet are adjacent to the two pole piecesrespectively whereby a substantial part of the magnetic flux of themagnet passes through said device, and in the other of said positions ofthe slide said two poles of the magnet are both adjacent to one of thetwo pole pieces.
 2. A key according to claim 1 wherein the casing ismade of plastics material.
 3. A key according to claim 2 wherein thecasing has on the inside two grooves disposed parallel to saiddirection, and the slide is provided with two rib-like projectionsslidable in respective grooves.
 4. A key according to claim 3 whereinthe slide is made of plastics material.
 5. A key according to claim 1wherein the magnet is generally U-shaped.
 6. A key according to claim 1wherein the two pole pieces are plate-shaped and made of magneticallysoft iron.
 7. A key according to claim 6 wherein one pole piece, asmeasured in said direction, is substantially longer than the other polepiece, and said one pole piece is arranged in the casing such that insaid other of said positions of the slide said two poles of the magnetare both adjacent to said one pole piece.
 8. A key according to claim 7wherein the end faces of the two pole pieces, which face towards oneanother, are parallel with one another and substantially perpendicularto said direction, said device in plate-shaped, and the two largesurfaces of said device extend perpendicular to said direction.
 9. A keyaccording to claim 8 wherein the cross section of one pole piece istapered in the direction of said device.
 10. A key according to claim 9wherein the end face of the tapered pole piece has at most one third ofthe cross-sectional area of the non-tapered part of said pole piece.